1. Field of the Invention
The invention relates to a silicon oxynitride film used for a semiconductor device, e.g. a thin film transistor, an MOS transistor, etc., and a method for forming the silicon oxynitride film. More particularly, the invention relates to a semiconductor device including the silicon oxynitride film and an oxide semiconductor thin film transistor.
2. Description of Related Art
Non-patent Literature No. 1 discloses that, in an oxide semiconductor thin film transistor (OTFT) having a channel layer formed with an In—Ga—Zn—O (IGZO) oxide semiconductor, a silicon oxide film (SiOx film) is deposited as a protection film (passivation layer) by a plasma chemical vapor deposition (CVD) method using a mixture gas of SiH4/N2O (referring to Table 1, the left column of page 228, for example).
It is disclosed in the Non-patent Literature No. 1 that the hydrogen in the silicon oxide film used as the protection film is assumed to be the cause of the shift of a threshold value Vth, which is one of the indexes for determining the reliability of the oxide semiconductor thin film transistor (referring to the left column of page 229, for example).
On the other hand, Patent Literature No. 1 discloses that a silicon oxide film (SiO2 film) containing no hydrogen can be formed by a plasma CVD method using a SiF4 gas to replace the conventional SiH4 gas source, using an O2 gas as the oxide gas, and using an N2 gas as the carry gas (referring to paragraph 0009, for example).